In the season premier of Third Watch on Monday 2 October.
One of the plotlines was a kidnapped guy was buried alive. They found him (alive) near the end, but one of the officers told the "saved by the bell" story.
You know, the one where dead people about to be buried had a string with a bell tied to their hand... the string was run up to the surface. If they were actually alive, they would just pull the string and a bell would ring... and they'd be saved. Hence, "Saved by the Bell".
It was really unrelated to the entire plot, it struck me as a time-killer, just something to fill 30 seconds or so... or MAYBE they are just testing us
Snopes debunking is at: http://www.snopes.com/spoons/fracture/1500.htm